Key Food tech questions

Explain the difference between HBV and LBVs?

• HBV proteins provide all of the essential amino acids for example,meat,dairy products and eggs.

• LBV proteins are missing one or more of the essential amino acids for example,beans ,lentils and nuts.

• Combining 2 or more LBV proteins together in a meal is known as protein complementation.Examples include beans on toast

Conduction

• Heat travels through solids from one molecule to the next by contact.

• The atoms vibrate and transfer heat energy

• Metals are good conductors=denser and heat is transferred more quickly

• Examples=Baking,boiling

Radiation

Heat travels directly onto food in straight lines.e.g grilling

Infared heat rays heat the surface of the food and are absorbed

In a microwave oven, electromagnetic waves transfer energy,

causing water molecules in the food to vibrate.

Examples=Microwaving,toasting

Convection

Heat travels through water (liquids) and air

Convection currents happen because hot air/water rises and cool air/water falls.

• This liquid or gas is in turn heated, expands becomes less dense and rises.

• This sets up a convection current.

Examples=Baking,stewing

Steaming

• Loss of water soluble vitamins (B and C ) is reduced because the food does not come into direct contact with water for example green vegetables

• Steam is very hot so food cooks quickly, which reduces water

  soluble vitamin loss.

Stir frying

A quick method of cooking so the water-soluble vitamins are retained.

Any vitamins and minerals which leach into the sauce/juices are retained.

Explain the term protein complementation

Combining low biological foods (LBV) together to produce high biological value (HBV) dishes/meals.

Low biological value protein foods lack one or more of the essential amino acids, but when combined together in a meal, they provide all of the essential amino acids and the meal/dish becomes high biological value.

• Beans on toast.

Peanut butter on toast or sandwich.

Explain the formation and function of gluten when making bread

• Gluten is found in flour

• When water is added to the flour, gliadin and glutenin form gluten

• Kneading helps the gluten strands become longer and stronger.

• The formation of gluten helps to trap air bubbles, which makes the

dough rise/gives dough a lighter texture.

• Gluten coagulates when cooked, which stabilises/sets the structure

of the risen bread.

Explain the process of emulsification when making mayonnaise

• Oil and vinegar are immiscible liquids/cannot combine.

• As the oil is added to the egg yolk, the mixture must be mixed

vigorously to form a fat-in-water emulsion.

• As the oil is whisked into the egg yolk the mixture thickens to give a

smooth and creamy consistency.

• Vinegar also acts as a preservative.

Explain the process of dextrinisation when baking a pizza

• Dextrinisation occurs when foods containing starch are cooked.

• It causes the outer layer of the starchy food to turn brown, ie the pizza crust and bottom of the base.

• The dry heat breaks the starch molecules into smaller groups of glucose molecules called dextrins.

• Dextrins give baked foods a baked/sweeter flavour.

Explain how the shortening process creates a crumbly texture

• Rubbing-in is used to rub fat (butter/lard/soft spread/block fat) into

flour.

• The fat creates a waterproof layer on the flour particles.

• When water is added, the waterproof layer restricts how much water can be absorbed, keeping gluten molecules short.

• Cold water should be used as it is absorbed less easily, keeping gluten molecules short.

Gelatinisation (custard)

Custard is made using custard powder or cornflour, which contain

starch.

• The custard powder/cornflour would be combined with milk before

being heated.

• The mixture would need to be stirred continuously to form a suspension/so the starch granules spread through the liquid.

• Stirring the sauce prevents starch sticking to the bottom of the saucepan causing lumps to form.

• When heated, the starch granules begin to absorb the milk.

• At 60°C, starch granules begin to soften and swell.

• At 80°C, the starch granules will burst releasing the starch into the

liquid.

• The starch thickens the mixture.

• At 100°C, gelatinisation/thickening is complete.

• As the custard cools down, a skin can develop and become a solid gel.

Explain the functional and chemical properties of the ingredients used in jam-making process

• Plums=Plums will provide flavour/plums are naturally sweet.

• Plums will add colour.

Lemon juice=Lemon juice provides citric acid.

• Lemon juice adds a sour/tangy flavour balance to the sweet sugar

and fruit.

Caramelisation

Sugar melts and turns brown when heated, making the cake golden

brown.

• Sugar is a disaccharide called sucrose, which is made from glucose

and fructose.

• Caramelisation occurs when sugar is heated between 160 °C and

170 °C.

• As it is heated, sugar (sucrose) molecules start to break up.

• As the heating continues, the hydrogen and oxygen atoms in the

sugar form water, which evaporates and is released as steam.

• The evaporation of water causes the colour of the sugar to gradually

change to golden brown, which enhances the colour of the cake,

particularly its surface.

Foams

Foams form when gas becomes trapped inside a liquid

When liquids containing proteins are agitated the proteins inside the liquid denature -this causes them to stretch and air becomes trapped in the liquid

When proteins coagulate this air becomes trapped creating a foam